In general, mobile communication systems have been developed for a purpose of providing communication while securing mobility of a user. The mobile communication systems have reached a stage where a high speed data communication service can be provided as well as voice communication on the strength of the rapid development of technologies.
Currently, a standardization operation from a 3rd Generation Partnership Project (3GPP) system to a Long Term Evolution (LTE) system is being progressed as one of next generation mobile communication systems. The LTE-A system has been developed to continuously improve the performance and implements a high speed packet-based communication having a transmission rate 3 to 10 times higher than a currently provided data transmission rate.
Further, a device to device communication has been continuously researched since the 2000's. A current mobile communication system can perform communication such as data transmission/reception through a wireless network of a Base Station (BS) and a wired network connected to the network for data transmission between User Equipments (UEs) within the same BS or neighboring BSs. Accordingly, the device to device communication has been researched to reduce loads and support effective communication between neighboring UEs when there is no wireless network. In addition, device to device communication which can be effectively performed in a state where there is no BS or the BS does not operate due to emergency or disaster is being researched.
Hereinafter, it must be understood that the LTE system refers to a meaning including both the LTE system and the LTE-A system.